The present disclosure relates to an active vibration isolator.
Widely known manufacturing apparatuses for various types of precision instruments, such as semiconductors and liquid crystal panels, include a movable stage on which a target to be manufactured is mounted to achieve accurate and high-speed positioning (see, for example, Japanese Patent No. 4970904).
Generally, an object mounted on such a stage is a precision instrument that is being manufactured, and is therefore vibration-sensitive. To address this problem, Japanese Patent No. 4970904 described above discloses the use of an active vibration isolator to reduce the transmission of vibrations from a floor as much as possible.
Specifically, Japanese Patent No. 4970904 described above discloses an active vibration isolator. The active vibration isolator includes a movable stage, a vibration isolation table (a surface plate) that supports the stage, a servo valve that imparts, to the vibration isolation table, a control force that reduces vibrations of the vibration isolation table, and a vibration sensor (an acceleration sensor) provided on the vibration isolation table. The active vibration isolator is configured to perform feedback control of an actuator based on a signal from the vibration sensor.
Japanese Patent No. 4970904 described above further discloses that to reduce vibrations caused by the movement of the stage as well as the vibrations transmitted from the floor, not only the feedback control described above but also the feed-forward control is performed.
Here, some of the vibrations caused by the movement of the stage result from a reactive force applied to the vibration isolation table in response to a thrust imparted to the stage, and the other vibrations result from the torque associated with the reactive force. To reduce the vibrations resulting from the reactive force, an acceleration imparted to the stage, for example, needs to be obtained.
On the other hand, to reduce the vibrations resulting from the torque, control needs to be performed based on a combination of the position of the stage and the reactive force applied to the vibration isolation table through the movement of the stage. To achieve better vibration control performance, the vibrations resulting from the torque also need to be reduced.
To satisfy the needs, the active vibration isolator described in Japanese Patent No. 4970904 estimates, and computes, the position and acceleration of the stage (moving object), and performs feed-forward control reflecting the estimation results, thereby reducing the vibrations resulting from the reactive force applied to the vibration isolation table and the vibrations resulting from the torque.